Human activity has strained a natural process for clearing the atmosphere, isle researchers find
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HILO » Scientists from Hawaii and California have found that Earth had for eons a finely tuned feedback mechanism that removed excess carbon from the atmosphere and turned it into seashells.
Now that subtle system has been overwhelmed by human influence, according to Richard Zeebe of the University of Hawaii and Ken Caldeira of the Carnegie Institution.
Using data from bubbles trapped in Antarctic ice cores, the researchers studied levels of carbon dioxide in the atmosphere over the past 610,000 years. Their findings show that vegetation is not the only way that nature cleanses carbon from the air.
Mild acid rain from the atmospheric carbon erodes rocks, sending calcium and carbon into the sea, where opihi, clams, mussels, corals and calcium-bearing plankton gobble up both chemicals, turning them to shells and skeletons that last for millions of years. But in the last 200 years, humans have put carbon dioxide into the air 14,000 times as fast as the average rate during the previous 600 millennia, Zeebe said.
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HILO » Mineral interactions on land and in the sea have a larger role in controlling global warming than the well-known ability of forests to take carbon dioxide out of the air, says a new study by two oceanographers.
But Richard Zeebe at the University of Hawaii and Ken Caldeira of the Carnegie Institution in Stanford, Calif., say that humans are putting so much carbon into the atmosphere that the mineral contribution to cleaning the air is being massively overwhelmed.
The lesson is that Earth's "carbon cycle" is now better understood, but minerals are not enough. Saving forests is still vital for fighting global warming, Zeebe said.
Zeebe and Caldeira published their work in the May edition of Nature Geoscience.
The long-term carbon cycle -- how carbon circulates in the air, water and minerals -- has been understood in a theoretical way for at least 25 years, Zeebe said, but until the 1990s there was not enough evidence to prove parts of the theory.
That changed with the dredging of sediment from the bottom of the ocean and the obtaining of more than 610,000 years of atmospheric samples from air bubbles trapped in Antarctic ice.
Researchers found carbon dioxide levels spiking up and down roughly every 100,000 years, which
Zeebe and Caldeira interpreted as showing mineral interactions.
Carbon dioxide in the air forms a mild acid rain that erodes rocks on land, he said. Carbon from the acid rain and calcium from the rocks are washed to the sea where clams, corals and calcium-bearing plankton gobble up both chemicals, turning them to shells and skeletons that last for millions of years, long after the creatures die.
This system is so efficient that the balance of carbon dioxide going into the air from volcanoes and other natural sources and carbon taken out of the air and water by clams and other creatures never was more than 2 percent out of balance.
Suddenly, in the last 200 years, humans have put carbon dioxide into the air 14,000 times as fast as the average rate during the previous 600,000 years, Zeebe said.
University of Hawaii scientist Richard E. Zeebe said the increase in acid rain is also increasing the acidity of the oceans, posing a threat to coral, he said.
"We have upset this so drastically that we cannot hope these (mineral) feedbacks will help us in the next few hundred years," he said.
Friday, May 9, 2008
University of Hawaii scientist Richard E. Zeebe said the increase in acid rain is also increasing the acidity of the oceans, posing a threat to coral. Originally, this article paraphrased him as saying it was killing coral. Also, researchers found carbon dioxide levels spiking up and down roughly every 100,000 years. This article also said carbon dioxide levels spike up and down every few hundred years.